[IRDA]: Fix rfcomm use-after-free

Adrian Bunk wrote:
> Commit 8de0a154 added the following
> use-after-free in net/bluetooth/rfcomm/tty.c:
>
> <--  snip  -->
>
> ...
> static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
> {
> ...
>         if (IS_ERR(dev->tty_dev)) {
>                 list_del(&dev->list);
>                 kfree(dev);
>                 return PTR_ERR(dev->tty_dev);
>         }
> ...
>
> <--  snip  -->
>
> Spotted by the Coverity checker.

really good catch. I fully overlooked that one. The attached patch
should fix it.
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bluetooth/rfcomm/tty.c

@@ -267,7 +267,7 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
 out:
 	write_unlock_bh(&rfcomm_dev_lock);
 
-	if (err) {
+	if (err < 0) {
 		kfree(dev);
 		return err;
 	}
@@ -275,9 +275,10 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
 	dev->tty_dev = tty_register_device(rfcomm_tty_driver, dev->id, NULL);
 
 	if (IS_ERR(dev->tty_dev)) {
+		err = PTR_ERR(dev->tty_dev);
 		list_del(&dev->list);
 		kfree(dev);
-		return PTR_ERR(dev->tty_dev);
+		return err;
 	}
 
 	return dev->id;